Insect attack of many fruits such as apples, citrus, and pears seriously affects the food industry. For instance, citrus greening is one of the most serious diseases threatening the $9.3 B Florida citrus industry. With no known cure, millions of trees have been removed from the citrus groves in order to prevent the spread of the disease. The loss of the citrus crop is estimated at 25% of a total $2.5 billion value for all U.S. citrus. The insect Asian Citrus Psyllid (ACP), carrier of bacterial species candidatus liberibacter asiaticus, spreads citrus greening, also known as the Huanglongbing (HLB) disease, primarily by feeding on citrus crops. In this process, the insect relies mainly on settling and olfactory cues. Current disease management methods have failed to stop, and are only partially successful in slowing, the ACP/HLB infestation due to a lack of known resistant cultivars, biological control agents, and cultural control options. Broad spectrum insecticides are currently the primary insect control options.
Particle film technology has emerged as a pesticide-less, environmentally friendly, and potentially economically sustainable approach to protect plants from insects. Although this technology has been used with some success for suppression of insect pests in apple and pear crops, it suffers from limitations, particularly: (i) insect attack in developing gaps created as a consequence of growth of existing leaves; (ii) insect attack on new unprotected flush and (iii) non-selective and poor adhesion of particles to leaves.
Particle films comprising hydrophilic and hydrophobic kaolin clays have been used for control of insects, such as, pear psylla, Cacopsylla pyricola Foerster, on pear (Prunus spp.)1 codling moth, Cydia pomonella (L.), on apple (Malus spp.)2; boll weevil, Anthonomus grandis grandis, Boheman, on cotton, Gossypium hirsutum L.,3 and European pear sucker, Cacopsylla pyri (L.). on pear (Prunus spp.)4. This technology is proving to be economically viable for suppression of pests in apples and pears2,5. Studies on the use of particle films for the suppression and biological effects of D. citri on citrus6-8 have also been reported to have varying degree of success.
The main effect of a particle film barrier on plant foliage is to interfere with the visual cues as well as ability of insects to settle, feed, move, and oviposit3, 9-11. In some cases, the film suspensions were found to be toxic to insects11, making toxicity an additional factor to be considered. Surface modified kaolin clay particle films have also been found to be effective against agricultural insects10,12. Surround WP (Engelhard Corp., Iselin, N.J.), a kaolin based formulation has shown to suppress infestations of nymph and adult D. citri in citrus trees by 31% and 61%, respectively, as compared with untreated trees8. Hall et al.6 have reported a similar cumulative reduction in infestation by D. citri of 78% on mature leaves, and 60% on flush shoots when compared to untreated trees. Similarly, significant reduction in the number of eggs and nymphs per flush (˜85%) in particle treated films is demonstrative of the effectiveness of the particle film approach in controlling the spread of HLB disease.
In spite of the success of the particle film technology, it suffers from major limitations. Puterka et al.11 reports that the mortality of adult pear psylla on particle treated foliage is low, since the adults are able to feed through the films, indicating the need for a continuous coating. In addition, the growth of the leaves after the application of particle film can also cause gaps to develop, making the leaves vulnerable to ACP attack. Another significant issue, especially with respect to the citrus crops, is the exclusive preference of adult females (D. citri) for fresh flush and unexpanded leaves for oviposits. This is a challenging issue requiring frequent film application. This necessitates an alternative protective methodology for protection between particle film applications. An additional limitation of the current particle film technology is the lack of rain fastness. Hall et al.6 have reported that more than 15 cm of cumulative rain completely negated the suppressive effect of Surround treatment. Combined with the visual observation that the particle film does not appear to adhere to the fresh flush as much it does to the mature leaves, this suggests that technological challenges must be overcome for extending the efficacy of particle film barrier to psyllid attack.
Insect repellents, such as plant derived essential oils, are an attractive means for pest management as they are considered minimum risk pesticides and exempt from EPA registration. In a recent report13, efficiency of crushed garlic chive leaves and garlic chive essential oil in repelling D. citri adults and a comparison to wild onion plants and crushed wild onion leaves has indicated promise. Similar mixture of components are found to be effective against other insect species14. In spite of the utility of essential oils to protect crops, they find limited application in fields due to the oils high volatility and lack of stability, which limits their effectiveness to shorter durations and necessitating frequent applications.
Hence there remains a need for an effective particle film technology that: (i) provides a continuous protection to the foliage during the growth and leaves expansion stages, thereby preventing psyllid attacks in developing gaps in particle films; and (ii) adheres to fresh flush and mature leaves and withstands weathering.    1. Puterka G J, Glenn D M M, Sekutowski D G, Unruh T R, Jones S K. Progress toward liquid formulations of particle films for insect and disease control in pear. Environmental Entomology 2000; 29(2):329-39    2. Unruh T R, Knight A L, Upton J, Glenn D M, Puterka G J. Particle films for suppression of the codling moth (Lepidoptera: Tortricidae) in apple and pear orchards. Journal Of Economic Entomology 2000; 93(3):737-43    3. Showier A T. Effects of kaolin-based particle film application on boll weevil (Coleoptera: Curculionidae) injury to cotton. Journal Of Economic Entomology 2002; 95(4):754-62    4. Daniel C, Pfammatter W, Kehrli P, Wyss E. Processed kaolin as an alternative insecticide against the European pear sucker, Cacopsylla pyri (L.). Journal of Applied Entomology 2005; 129(7):363-7    5. Knight A L, Christianson B A, Unruh T R Impacts of seasonal kaolin particle films on apple pest management. Canadian Entomologist 2001; 133(3):413-28    6. Hall D G, Lapointe S L, Wenninger E J. Effects of a particle film on biology and behavior of Diaphorina citri (Hemiptera: Psyllidae) and its infestations in citrus. Journal of Economic Entomology 2007; 100(3):847-54    7. Lapointe S L, McKenzie C L, Hall D G. Reduced oviposition by Diaprepes abbreviatus (Coleoptera: Curculionidae) and growth enhancement of citrus by surround particle film. Journal of Economic Entomology 2006; 99(1):109-16    8. McKenzie C L, Lapointe S L, Hunter W B, Puterka G J. Efficacy of Surround for control of Asian citrus psyllid on citrus. Arthropod Management Tests 27 2000; D8    9. Glenn D M, Puterka G J. Particle films: a new technology for agriculture. Horticultural Reviews 2005; 31:1-44    10. Liang G, Liu T X. Repellency of a kaolin particle film, surround, and a mineral oil, Sunspray oil, to silverleaf Whitefly (Homoptera: Aleyrodidae) on melon in the laboratory. Journal of Economic Entomology 2002; 95(2): 317-24    11. Puterka G J, Glenn D M, Pluta R C. Action of particle films on the biology and behavior of pear psylla (Homoptera: Psyllidae). Journal of Economic Entomology 2005; 98(6):2079-88    12. Eigenbrode S D, Ding H J, Neufeld J, Duetting P. Effects of hydrophilic and hydrophobic kaolin-based particle films on pea aphid (Homoptera: Aphididae) and its entomopathogen Pandora neoaphidis (Entomophthorales: Entomophthoraceae). Journal of Economic Entomology 2006; 99(1):23-31    13. Mann R S, Rouseff R L, Smoot J M, Castle W S, Stelinski L L. Sulfur volatiles from Allium spp. affect Asian citrus psyllid, Diaphorina citri Kuwayama Hemiptera: Psyllidae), response to citrus volatiles. Bulletin of Entomological Research 2010; doi: 10.1017/S0007485310000222:1-9    14. Podskalska H, Ruzicka J, Hoskovec M, Salek M. Use of infochemicals to attract carrion beetles into pitfall traps. Entomologia Experimentalis Et Applicata 2009; 132(1):59-64